I assume you are speaking of ripping Video and Audio from DVDs, right? If so, the reason this separation of sound and movie occurs is because the sound and video components are separate within the DVD. WHen you rip the video file to your hard drive, you get ONLY that video, no sound. You would have to
-Rip the audio separately and merge it, as Ann said, or
-Find a program that letd you rip both at the same time and merges them automatically.
This isn't an area with which I am terribly familiar, but I know that when I rip things off of DVDs, there are several separatate video and audio tracks to choose from, not just one.